The letters, which sound dire warnings about the existential threat climate change poses, establish immediate, concrete commitments that BlackRock is making toward more sustainable investing and product offerings.

Many of the announced changes go into effect in the next few months.

‘Significant Reallocation Of Capital’

In its client letter, BlackRock identified two key risks from climate change: the "physical risk" associated with environmental changes, such as rising temperatures and sea levels; and "transition risk" associated with society moving to a low-carbon economy.

This transition may not be cheap or easy for companies, and it could and likely will cut into their bottom lines. But it will happen regardless, says Fink, because it must: "In the near future—and sooner than most anticipate—there will be a significant reallocation of capital."

"I believe we are on the edge of a fundamental reshaping of finance," he added.

Doubling ESG Lineup

Among the changes announced, BlackRock intends to double its current lineup of ESG ETFs, up to a projected 150 products worldwide.

Many of these new ETFs will be sustainable versions of its flagship index products, though which indexes or products were not specified in the announcements.

Currently, iShares offers 14 ESG ETFs in the U.S., totaling over $10.4 billion in assets under management, or more than half of all assets invested in ESG ETFs:

Some ETFs will focus on screening out specific sectors or companies that investors find objectionable—so-called "exclusionary screened" ETFs that historically had dominated ESG product offerings.

Other ETFs will provide exposure to high-ESG-ranked companies while simultaneously attempting to match the performance of traditional market-cap-weighted benchmarks. This product category has found particular success recently with the launch of funds like the $1.86 billion iShares ESG MSCI USA Leaders ETF (SUSL).